This invention relates to a method and apparatus for RACH preamble detection. While the invention is particularly directed to the art of telecommunications, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications.
By way of background, The 3rd Generation Partnership Project (3GPP) is a collaboration agreement that was founded in December 1998. The scope of 3GPP is to make a globally applicable third generation (3G) mobile phone system specifications for UMTS (3G systems based on the evolved GSM core network and the Universal Terrestrial Radio Access (UTRA) in FDD and TDD mode and GSM including evolved GSM radio access technologies (GPRS, EDGE).
The 3GPP standardization department is currently working on the 3G Long Term Evolution (LTE). See, for example, 3GPP TR 25.912 and 25.913. Important parts of such a long-term evolution include reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operator. In order to achieve this, an evolution of the radio interface as well as the radio network architecture will be considered. Considering a desire for even higher data rates and also taking into account future additional 3G spectrum allocations the long-term 3GPP evolution will include an evolution towards support for wider transmission bandwidth than 5 MHz At the same time, support for transmission bandwidths of 5 MHz and less than 5 MHz will be investigated in order to allow for more flexibility in whichever frequency bands the system may be deployed.
The Random Access Channel (RACH) is a contention-based channel for initial uplink transmission, i.e., from UE (User Equipment) to NodeB (base station). This channel can be used for several purposes. The RACH function is different depending on the technology of the system. The RACH can be used to access the network, to request resources, to carry control information, to be the reference of adjusting the time offset of the uplink, to be the reference of adjusting the transmitted power, and to transmit small amounts of data. Contention resolution is a key feature of the random access channel. Many UE can attend to access a same base simultaneously, leading to collisions.
Several options are available for multiplexing between the RACH and scheduled-based channels, Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM), and Code Division Multiplexing (CDM).
The RACH format in the Universal Mobile Telecommunications System (UMTS) LTE system generally includes a 0.1 ms cyclic prefix, a 0.8 ms RACH preamble and a 0.1 ms guard time. The LTE system is designed to process the 0.8 ms RACH preamble collectively to enable more processing gain for the preamble detection. The collective processing of the 0.8 ms RACH preamble requires a long fast Fourier transform (FFT) to convert the time domain to frequency domain preamble signals. The length of the long FFT depends on the number of samples in the 0.8 ms length, which is inversely proportional to the duration of the each sampling. For example, the number of samples in a 5 MHz system is 6144 in the 0.8 ms duration. Thus, it requires a FFT length of 6144 to process. Since the RACH information embeds in the central 1.08 MHz of the overall spectrum (e.g., 5 MHz), the RACH information needs to be extracted out from the frequency domain output of the Long FFT processing before proceeding to the detection.
The present invention contemplates a new and improved method and apparatus that resolves the above-referenced difficulties and others.